My wife is the type to read everything she can about a place before we go there the first time.
She says that she read once that with small children, you should consider going to one of the other parks (Epcot, MGM, AK) before you go to the Magic Kingdom because if you bring a small child to MK first, they may become bored when you go to one of the other parks the second day.
I don't know if we personally share that opinion, but we did read it from a supposed expert.